When we discuss our Immune system, the two terms then strike our minds are the ‘antigen’ and the ‘antibody’. Antigen as we all know is the foreign particle that invades our body’s mechanism and thus tries to weaken our immune system.
On the contrary, Antibodies are present in one’s body and work as the defender while fighting against the foreign particle or any microorganism that can be harmful to the body in any way.
In this article, we will be going to discuss the type of antibodies, which are also known as “Immunoglobulins” or “Igs”, along with their types, structure,s, and functions. Immunoglobulins are the glycoproteins, which are produced against the antigen that has triggered the body’s immune system and thus initiate the action against the same (antigen).
Structure of the Antibody
Basically, the antibody has the ‘Y’ shape structure, which as the weight of the 150 KD, this ‘Y’ shapes structure is composed of the two heavy chains and the two light chains, the heavy chains weigh – 50 KD each while light chains weigh – 25 KD each, these chains are connected through the disulfide bonds.
Furthermore, antibodies are divided into – a variable region and a constant region. A variable region is known for its antigen-binding site, which is highly specific and this has the portion, known as the fragment antigen-binding (Fab) that is very selective with the antigen. Each antibody has two Fab to bind to the two identical epitopes.
A constant region plays the role in initiating the immune reaction as it has the region known as fragment crystallization (Fc) that binds to the surface receptors of the circulating macrophages, Nk cells, and WBCs. Additionally, there are also the Two Hinge regions, that is also connected with the Fab and Fc portions of an antibody.
Types of Antibodies
There are five types of antibodies, that play their crucial at different stages of immune reaction or whenever required. These five types are IgG, IgM, IgE, IgG, IgA.
IgG or Immunoglobulin G acquires a whopping amount of 75% among all the immunoglobulins in serum. IgG is the first Ig that crosses the placenta in pregnant women and delivers passive immunity to the growing fetus So, this is the dominant antibody and is majorly found in lymph and blood. It has four subclasses like IgG1, IgG2, IgG3, IgG4.
IgG has a small size and is a monomer, and so highly diffusible and plays a significant role in phagocytosis or triggers the antibody-dependent cell-mediated cytotoxicity (ADCC) response. The phagocytosis is followed by opsonization, which is also kicked by the IgG. It has a molecular weight: 150,000 KD.
IgM or Immunoglobulin M is the first antibody that is been synthesized in response to the invasion of the foreign particle or microorganisms attacking the body. It accounts for around 5% of the total Igs and is the largest antibody. It is present as a pentamer, or in a group of bounded five IgM monomers. This Ig has a short lifespan of 5 days only. It is highly effective against microbes as it causes bacteriolysis and agglutination. It has a molecular weight: 900,000 KD.
IgA or Immunoglobulin A, this Ig accounts for 6 percent of the total antibodies present in serum and is the second most common type. It is in the monomeric form. It has a half-life of five days. IgA is secreted in mucus, saliva, tears, colostrum, as it is found in secretions secretory. It has two subtypes IgA1 and IgA2. Therefore, the primary role of This Ig exists to defend against the ingested and inhaled harmful particles. It has a molecular weight: 320,000 KD (secretory).
IgE or Immunoglobulin E, is the most widespread immunoglobulin that accounts for only o.002% of all the Igs, though but highly active during protection against parasites, as well especially under allergic conditions like bronchopulmonary aspergillosis. It has a molecular weight: 200,000 KD.
IgD or Immunoglobulin D is present on the surface of B cells, it plays the role in suppressing the antibody producing cells and thus check the production of antibodies. It accounts for only 0.2% of the total Igs in serum. It has a molecular weight: 180,000 KD.